Um I am not sure of an exact recipe....My friend takes whole leaves with her when they are hiking in case any ankles are hurt....she said she just puts the fresh leaf on the site and uses a wrap to hold it in place.
Does that help?

The traditional way that I was taught to use comfrey for sprains was to pound the leaves & roots to release the slimy, healing juices then apply the mash to the affected body part. Use as much plant matter as needed to cover the affected area.

Where a cast or conventional medical assistance is not available, comfrey is pounded with sand or any clean, finely crushed matter to make a primitive cast, but only if the skin is unbroken. And the patient is also encouraged to drink comfrey leaf tea --a practice that alarms many who now believe comfrey can cause liver disease.

With topical herbal treatments, I've found that consistent use immediately after the injury brings about best results, so I would probably try to keep it up for a couple of weeks. But when I sprained my ankle as a child, my mother only made me wear the 'comfrey cast' for a few days.

Please be mindful of the fact that comfrey leaves have hairs on them that can be irritating, so you may want to sandwich the comfrey paste between 2 thin layers of gauze before applying it.

Modern shortcuts include regularly washing the wound with an infusion of comfrey; laying a cloth soaked with comfrey infusion on the area regularly; or simply applying comfrey tincture topically & allowing it to dry.

All of this assumes that you are well aware of the controversy surrounding comfrey's safety. If not, a quick search of the Herbalism forum for "comfrey" will fill you in on the hot debate & give you some information with which to make your own decision.